M68HC08 datasheet(104/288 Pages) FREESCALE

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System Integration Module (SIM)

Data Sheet

MC68HC908BD48 — Rev. 2.1

104

System Integration Module (SIM)

Freescale Semiconductor

7.6.3 Reset

All reset sources always have equal and highest priority and cannot be

arbitrated.

7.6.4 Break Interrupts

The break module can stop normal program flow at a software-

programmable break point by asserting its break interrupt output (see

Section 20. Break Module (BRK)). The SIM puts the CPU into the

break state by forcing it to the SWI vector location. Refer to the break

interrupt subsection of each module to see how each module is affected

by the break state.

7.6.5 Status Flag Protection in Break Mode

The SIM controls whether status flags contained in other modules can

be cleared during break mode. The user can select whether flags are

protected from being cleared by properly initializing the break clear flag

enable bit (BCFE) in the SIM break flag control register (SBFCR).

Protecting flags in break mode ensures that set flags will not be cleared

while in break mode. This protection allows registers to be freely read

and written during break mode without losing status flag information.

Setting the BCFE bit enables the clearing mechanisms. Once cleared in

break mode, a flag remains cleared even when break mode is exited.

Status flags with a two-step clearing mechanism — for example, a read

of one register followed by the read or write of another — are protected,

even when the first step is accomplished prior to entering break mode.

Upon leaving break mode, execution of the second step will clear the flag

as normal.

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